The present invention relates to noise isolation structures, and more particularly, to ferroelectric and ferromagnetic noise isolation structures, devices and system architectures.
System miniaturization and high performance (higher bandwidth, functionality and lower power requirements) demand integrated heterogeneous device architectures. Logic, memory and analog devices are continuously integrated with three-dimensional packaging. On the other hand, passive and active functions are migrating to wafer scale to integrate the digital and mixed signal subsystems in small form factors with leading edge performance. Three-dimensional integration with through-vias and wafer-to-wafer bonding, and embedded wafer level functions is evolving as a major paradigm shift to address system integration demands.
Noise isolation is a major concern for integrated mixed signal systems. High frequency digital signals induce noise into the sensitive low-power RF circuits. Integration of dissimilar signals requires large isolation between them. For multiple voltage levels, distributing power to the digital and RF circuits, while simultaneously maintaining isolation and low EMI, can be a major challenge. As systems migrate to three dimensional structures with smaller form factors, this problem is further aggravated.
Currently, noise isolation is achieved with RF chokes, EMI shields, ferrite absorbers, patterned ground planes creating electronic band gap (EBG) structures, and the like. These structures are limited by current material systems leading to bulky structures that cannot be easily integrated into thin film build-up structures and cannot isolate at higher frequencies. In addition, tunability is not easily achieved with the current materials.
Industry is migrating towards integration of heterogeneous functions with smaller form factor. FIG. 1 shows an embodiment of an exemplary system for Ultra Mobile Computing Applications to support wireless communication for mobility by integrating several standards, such as Bluetooth, WLAN and WIMAX, to support high speed computing. An implementation of such a system would require the integration of several new technologies, in addition to the integration of dissimilar die such as RF, digital, memory and sensors. To reduce system size, several semiconductor and system companies are pursuing three-dimensional stacking of die and packages in addition to planar thin film integration. The primary goal of the new technologies is to reduce size (area and height), increase performance and reduce cost. A major problem in such highly integrated systems is electromagnetic interference (EMI), which causes significant noise coupling between the digital and RF die. Both horizontal and vertical noise isolation is required to reduce electromagnetic interference.
EMI in such integrated systems can occur in two directions, namely along a horizontal direction through a substrate and along a vertical direction between stacked devices (die). A major source of coupling along the horizontal direction is through the power delivery network, which can be mitigated using electromagnetic bandgap (EBG) structures. This is discussed by in U.S. Pat. No. 7,215,301, entitled “Electromagnetic bandgap structure for isolation in mixed-signal systems,” issue May 8, 2007.
EBG structures provide RF isolation levels of −100 dB or better in an area of 1 cm2 with a bandwidth from 1 to 10 GHz, which is better than any other technology that has been reported so far. An example of an exemplary EBG structure and its response are respectively shown in FIGS. 2a and 2b. EBG structures depend upon the periodicity of a unit cell along a lateral direction to generate their bandgap response, as shown in FIGS. 2a and 2b. EBG structures in their present form, however, cannot be used to isolate stacked die or devices to minimize vertical noise coupling, due to their size. The vertical noise coupling between RF and digital die has been identified as a major bottleneck with regard to three-dimensional integration. Other approach is to reduce EMI noise by using active devices such as EMI filter chips.
It would be desirable to have simple thin films made of ferroelectric and ferromagnetic noise isolation structures that reduce electromagnetic interference and noise in integrated circuit devices and system architectures.